Memory formation and habit formation are two qualitatively different retention processes based on separate neural mechanisms. Recent developmental studies in monkeys have indicated that these two systems of retention are developmentally dissociable, with the habit system maturing earlier than the memory system. On the evidence that the libic memory system is not fully developed in infants, we have begun to prepare monkeys with neonatal removal of this system to see how cognitive, emotional, and social behavior develops in animals whose global amnesia might persist from infancy through adulthood. Animals with neonatal removal of area TE, a higher-order station of the visual system, are serving as controls. Preliminary results indicate that at two and six months of age, monkeys with neonatal limbic lesions display abnormal social behavior, whereas the operated controls are essentially unimpaired relative to normal infants. Examined at three months of age, animals with neonatal ablation of area TE showed a transient impairment of habit formation (compared to permanent impairment in adults with the same lesion), whereas the habit formation of animals with neonatal limbic lesions was intact (just as in adults). Interestingly, data on both normal and operated infants are suggestive of sexual dimorphism in the development of the habit system. At ten months of age, the animals with neonatal limbic lesions are markedly impaired in memory formation (just like adults), whereas the operated controls showed significant functional sparing of memory (compared with adults). Our tentative conclusion is not only that early and late brain damage have different consequences but also that the direction of the difference depends on the locus of the lesion (cortical or subcortical), the type of retention process examined (memory or habit), and the sex of the subject.